Index: modules/system/theme.api.php
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/theme.api.php,v
retrieving revision 1.1
diff -u -r1.1 theme.api.php
--- modules/system/theme.api.php	27 Feb 2010 09:24:09 -0000	1.1
+++ modules/system/theme.api.php	23 Apr 2010 20:02:49 -0000
@@ -93,3 +93,30 @@
     '#description'   => t('Show a trail of links from the homepage to the current page.'),
   );
 }
+
+/**
+ * Respond to themes being enabled.
+ *
+ * @param array $theme_list
+ *   Array containing the names of the themes being enabled.
+ *
+ * @see theme_enable()
+ */
+function hook_themes_enabled($theme_list) {
+  foreach ($theme_list as $theme) {
+    block_theme_initialize($theme);
+  }
+}
+
+/**
+ * Respond to themes being disabled.
+ *
+ * @param array $theme_list
+ *   Array containing the names of the themes being disabled.
+ *
+ * @see theme_disable()
+ */
+function hook_themes_disabled($theme_list) {
+ // Clear all update module caches.
+  _update_cache_clear();
+}